Temperature monitoring circuit

Abstract

A temperature monitoring circuit includes a negative temperature coefficient (NTC) resistor, a zener diode, an alarm, a silicon controlled rectifier. A first terminal of the NTC resistor is connected to a power supply through a first resistor. A second terminal of the NTC resistor is grounded. A cathode of the zener diode is connected to a node between the NTC resistor and the first resistor. An anode is grounded through a second resistor. A first terminal of the alarm is connected to the cathode of the zener diode, and is grounded through a third and fourth resistors in series. A cathode of the silicon controlled rectifier is connected to the anode of the zener diode. An anode of the silicon controlled rectifier is connected to a second terminal of the alarm. A control terminal of the silicon controlled rectifier is connected to a node between the third and fourth resistors.

What is claimed is: 
     
       1. A temperature monitoring circuit comprising:
 a negative temperature coefficient (NTC) resistor, wherein a first terminal of the NTC resistor is connected to a power supply through a first resistor, a second terminal of the NTC is grounded; 
 a zener diode, wherein a cathode of the zener diode is connected to a node between the NTC resistor and the first resistor, an anode of the zener diode is grounded through a second resistor; 
 an alarm, wherein a first terminal of the alarm is connected to the cathode of the zener diode, and is grounded through a third resistor and a fourth resistor connected in series; and 
 a silicon controlled rectifier, wherein a cathode of the silicon controlled rectifier is connected to the anode of the zener diode, an anode of the silicon controlled rectifier is connected to a second terminal of the alarm, a control terminal of the silicon controlled rectifier is connected to a node between the third resistor and the fourth resistor. 
 
     
     
       2. The temperature monitoring circuit of  claim 1 , wherein the alarm is a light-emitting diode, an anode of the light-emitting diode is the first terminal of the alarm, a cathode of the light-emitting diode is the second terminal of the alarm. 
     
     
       3. The temperature monitoring circuit of  claim 1 , wherein the alarm is a buzzer, a first terminal of the buzzer is the first terminal of the alarm, a second terminal of the buzzer is the second terminal of the alarm. 
     
     
       4. A temperature monitoring circuit comprising:
 a negative temperature coefficient (NTC) resistor, wherein a first terminal of the NTC resistor is connected to a power supply through a first resistor, a second terminal of the NTC resistor is grounded; 
 a zener diode, wherein a cathode of the zener diode is connected to a node between the NTC resistor and the first resistor, an anode of the zener diode is grounded through a second resistor; 
 a fan, wherein a first terminal of the fan is grounded through a third resistor and a fourth resistor connected in series; and 
 a silicon controlled rectifier, wherein a cathode of the silicon controlled rectifier is connected to the anode of the zener diode, an anode of the silicon controlled rectifier is connected to a second terminal of the fan, a control terminal of the silicon controlled rectifier is connected to a node between the third resistor and the fourth resistor. 
 
     
     
       5. The temperature monitoring circuit of  claim 4 , further comprising an alarm connected to the fan in parallel. 
     
     
       6. The temperature monitoring circuit of  claim 5 , wherein the alarm is a light-emitting diode, an anode of the light-emitting diode is connected to the first terminal of the fan, a cathode of the light-emitting diode is connected to the second terminal of the fan. 
     
     
       7. The temperature monitoring circuit of  claim 5 , wherein the alarm is a buzzer.